The present invention relates to a presensitized plate for use in making a lithographic printing plate which makes it possible to perform printing without using dampening water.
There have been proposed various kinds of presensitized plates for use in making lithographic printing plates requiring no dampening water (hereunder referred to as "water-less PS plates) for performing lithographic printing operations without using any dampening water. Among them, those comprising, on a substrate, a light-sensitive resin layer and a silicone rubber layer in this order show quite excellent properties, as disclosed in, for instance, Japanese Patent Publication for Opposition Purpose (hereinafter referred to as "J.P. KOKOKU") Nos. Sho 54-26923 and Sho 55-22781.
The silicone rubber layer used in these water-less PS plates are in general obtained by partially cross-linking, with a cross-linking agent, a high molecular weight polymer comprising a polysiloxane structure as its principal skeleton. On the other hand, there have been used, as a light-sensitive resin layer, photopolymerizable light-sensitive compositions, photodimerizable light-sensitive compositions or diazo type light-sensitive compositions, which are cured upon exposure in case of positive-working presensitized plates for use in making lithographic printing plates (hereunder referred to as "PS plates"). In general, to form images on these PS plates having the foregoing layer structure, the light-sensitive resin layer is cured by irradiating it with light, if necessary, by causing photoadhesion at the boundary between the light-sensitive layer and the silicone rubber layer provided thereon during the exposure to light, for firmly bonding them and for simultaneously preventing the penetration of a developer into the plate and hence the dissolution of the light-sensitive layer, whereby forming non-image areas comprising the silicone rubber layer. On the other hand, image areas can be formed by permeating the developer into the light-sensitive layer through the silicone rubber layer to dissolve out a part or whole of the uncured light-sensitive layer and then removing the silicone rubber layer on the uncured light-sensitive layer by means of a physical force. It is important to prevent the removal of the non-image areas during the development and subsequent printing operations, by firmly adhering the light-sensitive resin layer to the silicone rubber layer when the images are formed in such a manner. For this reason, various light-sensitive compositions have been proposed. For instance, a photopolymerizable light-sensitive composition disclosed in Japanese Patent Unexamined Publication (hereunder referred to as "J.P. KOKAI") Nos. Sho 63-253949 and Sho 63-280250, in which an allyl methacrylate copolymer is used as a binder, makes it possible to ensure the adhesion between a light-sensitive layer and a silicone rubber layer to some extent if the composition for the silicone rubber layer to be applied onto the layer of the light-sensitive composition is properly selected and thus to be able to form images. However, the quality of the images thus formed is not still sufficient.